The present invention is generally related to optical fiber layers and, more particularly, to one or more optical fiber layers that buffer the optical fiber and enhance microbend resistance and low-temperature performance of the optical fiber.
Optical fibers are now in widespread use as communication media. Conventional optical fibers typically include a glassy core and one or more coating layers surrounding the core. Surrounding the coating layers is at least one further layer of material, commonly referred to as a buffer or outer layer, which protects the fiber from damage and which provides the appropriate amount of stiffness to the fiber. The outer layer usually is mechanically stripped away from the fiber when the fiber is connected to an optical fiber connector. Normally, the outer layer is composed of a thermoplastic polymeric material, which is extruded directly over the coated optical fiber. Common materials used to form outer layers include polyvinyl chloride (PVC), nylon, and polyesters, fluropolymers, etc.
In many cases, it is necessary that the thermoplastic outer layer be removable without disturbing the optical fiber coatings. This is facilitated by the use of an inner layer, which allows the removal the outer buffer material without removing the coating. The inner layer also facilitates better temperature performance at low temperatures by serving as a compliant layer between the hard thermoplastic buffer material and the optical fiber.
Conventional dual-layered tight buffered optical fibers have an inner layer made of polyethylene/ethylene-ethyl acrylate (PE/EEA) copolymer. However, this material has several disadvantages (U.S. Pat. No. 5,684,910). One disadvantage of using PE/EEA is that, being a thermoplastic, the viscosity of the PE/EEA copolymer decreases when the outer layer is applied thereby causing the PE/EEA copolymer to become much less viscous and more fluid-like. The impact of this is that any volatilization coming from the optical fiber coating, whether it is moisture or low molecular weight components, may cause the formation of bubbles in the inner layer. Bubbles, depending on size and frequency, will cause attenuation to increase in the optical fiber, which is typically seen at low temperatures (e.g., xe2x88x9220xc2x0 C.). If the bubbles are severe, an increase in attenuation may occur at room temperature (xcx9c21xc2x0 C.).
An additional problem caused by the material is that the attenuation of the optical fiber cable increases at temperatures below xe2x88x9220xc2x0 C. The increased attenuation at temperatures below xe2x88x9220xc2x0 C. can be attributed to the increase in the elastic modulus of the EEA. Therefore, EEA does not satisfy the need for inner layers having minimal variation in elastic modulus over the temperature range of xe2x88x9240xc2x0 C. to 80xc2x0 C.
The critical nature of the inner layer becomes even more apparent when applied to newer, higher bandwidth fibers (e.g., 50 micron multi-mode fibers with reduced differential modal dispersion). These fibers and others have higher bandwidths but generally are more microbend sensitive.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
Briefly described, embodiments of the present invention provide for buffered optical fibers and methods for fabricating them. A representative buffered optical fiber in accordance with the present invention includes an optical fiber through which optical signals can be transmitted and a layer comprising an ultra-violet (UV) curable acrylate material that surrounds the optical fiber and protects the core of the optical fiber from microbending forces.
A representative method for fabricating the buffered optical fiber includes: advancing a fiber core through a coating head oriented in a vertical position; the coating head placing an inner layer on the optical fiber, the inner layer being an ultra-violet (UV) curable acrylate material; advancing the optical fiber having the inner layer thereon through a UV oven oriented in a vertical position, the UV oven curing the UV curable acrylate material; and advancing the optical fiber having the cured inner layer thereon into a horizontal processing system using a transition sheave.
Other features and advantages of the present invention will become apparent to one skilled in the art upon examination of the following drawings and detailed description.